Markov chain approach to analyze the dynamics of pathogen fecal shedding - Example of Listeria monocytogenes shedding in a herd of dairy cattle

Department of Food Science, Cornell University, Итак, New York, United States
Journal of Theoretical Biology (Impact Factor: 2.3). 04/2007; 245(1):44-58. DOI: 10.1016/j.jtbi.2006.09.031
Source: PubMed

ABSTRACT Fecal shedding is an important mechanism of spreading of a number of human and animal pathogens. Understanding of the dynamics of pathogen fecal shedding is critical to be able to control or prevent the spread of diseases caused by these pathogens. The objective of this study was to develop a model for analysis of the dynamics of pathogen fecal shedding. Fecal shedding of Listeria monocytogenes in dairy cattle was used as a model system. A Markov chain model (MCM) with two states, shedding and non-shedding, has been developed for overall L. monocytogenes fecal shedding (all L. monocytogenes subtypes) and fecal shedding of three L. monocytogenes subtypes (ribotypes 1058A, 1039E and 1042B) using data from one study farm. The matrices of conditional probabilities of transition between shedding and non-shedding states for different sets of covariates have been estimated by application of logistic regression. The covariate-specific matrices of conditional probabilities, describing the presence of different risk factors, were used to estimate (i) the stationary prevalence of dairy cows that shed any L. monocytogenes subtype or ribotypes 1058A, 1039E, and 1042B, (ii) the duration of overall and subtype specific fecal shedding, and (iii) the duration of periods without shedding. A non-homogeneous MCM was constructed to study how the prevalence of fecal shedders changes over time. The model was validated with data from the study farm and published literature. The results of our modeling work indicated that (i) the prevalence of L. monocytogenes fecal shedders varies over time and can be higher than 90%, (ii) L. monocytogenes subtypes exhibit different dynamics of fecal shedding, (iii) the dynamics of L. monocytogenes fecal shedding are highly associated with contamination of silage (fermented feed) and cows' exposure to stress, and (iv) the developed approach can be readily used to study the dynamics of fecal shedding in other pathogen-host-environment systems.

  • Source
    • "However, it is important to bear in mind the challenges in studying transmission of this pathogen related to the overall diversity and variability of L. monocytogenes, even within a single dairy herd, particularly considering the well supported strain variability in L. monocytogenes virulence (Nightingale et al., 2005; Roche et al., 2005). Therefore, the extensive sampling conducted in this study provided particularly valuable data for a better understanding of L. monocytogenes shedding in cattle, and has also formed the basis for a mathematical model on pathogen shedding (Ivanek et al., 2007). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Fecal shedding of Listeria monocytogenes poses a risk for contamination of animal feed and agricultural environments and raw food at the pre-harvest stages of food production. To be able to reduce these risks it is critical to improve understanding of the epidemiology of L. monocytogenes shedding in feces. The objective of this study was to assess the daily variability of fecal shedding and its association with individual animal (lactation number and the day of current lactation) and environmental (feed) risk factors. That was achieved by application of longitudinal daily sample collection in a herd of dairy cattle and molecular characterization of isolated L. monocytogenes. Fecal samples (25) and silage samples (2) were collected daily during two 2-week periods and one 5-day period. L. monocytogenes was isolated from 255 out of 825 (31%) fecal samples on 24 out of 33 (73%) days, and from 25 out of 66 (38%) silage samples on 16 out of 33 (48%) days. Ninety-four percent of cows excreted L. monocytogenes in feces at least once during the study period. Our data analyses indicated that (i) the prevalence and incidence risk of L. monocytogenes fecal shedding in cattle vary considerably over time, from 0 to 100%, and both are associated with contamination of silage, (ii) L. monocytogenes fecal shedding in cattle could occur as part of an outbreak or as an isolated sporadic case, (iii) L. monocytogenes subtypes associated with human infections are commonly isolated from cattle feces and silage, and (iv) a single cow can harbor more than one L. monocytogenes subtype on any given day. Although limited to a single dairy cattle herd, these findings provide a significant advancement in the understanding of the epidemiology of L. monocytogenes fecal shedding in dairy cattle.
    Preventive Veterinary Medicine 09/2007; 80(4):287-305. DOI:10.1016/j.prevetmed.2007.03.005 · 2.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: NOTE: An effective introduction to Markov chains and some of their computational science applications can be accomplished by covering the first two parts, "Scientific Questions" and "Computational Models," and omitting the third on "Bioinformatics and Markov Chains." Exercise 1 and Projects 1-5 are accessible with only this background. The third part provides the necessary background for Exercises 2 and 3 and Projects 6-10. The sections entitled "The Area" and "High Performance Computing and Bioinformatics" of that part can be covered on their own as an overview of the need for high performance computing in this important new area of biology and computational science.
  • [Show abstract] [Hide abstract]
    ABSTRACT: As a part of the Sanitary and Phytosanitary (SPS) agreement, the World Trade Organization requires that member countries establish SPS measures on the basis of an appropriate risk assessment. In addition, many governments use risk assessment in their management of food safety. Consequently, a number of risk assessments for different foodborne pathogens have been conducted. Risk assessments have also been successfully used as a research tool. While, historically, risk assessments are typically initiated by government agencies, university-based researchers are increasingly becoming involved in risk assessments. The purpose of this article is to illustrate the role that university researchers can play in the development and refinement of food safety risk assessments, including possible roles in (1) de novo development or refinement of risk assessment (including farm-to-table risk assessment), (2) data collection supporting risk assessments, and (3) development of new methodological techniques. Transmission of the foodborne pathogen Listeria monocytogenes through the food production chain and risk assessments addressing transmission of this pathogen are used as an example to highlight the roles of university researchers in food safety risk assessments.
    Foodborne Pathogens and Disease 02/2007; 4(4):527-37. DOI:10.1089/fpd.2007.0012 · 2.09 Impact Factor
Show more